Traditionally, the bands between analog television broadcast signals were not used for transmissions due to possible destructive interference with the spectrally adjacent television broadcast signals. For example, FIG. 1A shows an analog television spectrum 100 having bands TVx and TVy each occupied by an analog signal, and spectral regions x1, x2, y1, and y2 which are unavailable for transmission due to possible interference with signals in bands TVx and TVy. FIG. 1A further illustrates a minimum spacing “z” (on a band frequency scale) by which two analog transmissions must be distanced from each other to minimize interference.
However, digital signal transmission, such as digital television broadcasts, do not have the same risk of interference from signal transmissions on adjacent bands. Since television is now predominately broadcast in digital format, unused bands that were previously unavailable (colloquially known as “white spaces”) can be used for signal transmission without interfering with adjacent bands. For example, FIG. 1B shows a digital television spectrum 100a comparable to that of FIG. 1A, having a white space “a” in place of spectral region x1, a white space “b” in place of spectral regions x2 and y2, and a white space c in place of spectral region y2. FIG. 1C shows an alternative digital radio spectrum 101 having bands 102a-102f occupied by a digital signal, and available white spaces 103a-103g. The Federal Communications Commission (FCC), which regulates such transmissions, has extensively discussed allowing unlicensed signal transmissions in the previously restricted white spaces. For example, the FCC has proposed new rules for use of unlicensed spectrum space that include requirements for querying a geolocation database.
The FCC has opened up new frequency bands for unlicensed use of the television and radio spectrum that will coexist with digital television (e.g., from 512 MHz to 698 MHz). These television white space bands will be regulated to ensure that equipment does not interfere with incumbent transmitters (like television broadcast channels). The FCC has defined the use of a geolocation database and spectral sensing as mechanisms to protect transmissions from the incumbent transmitters. Geolocation requires that a device intending to transmit in the television white space query a central database for available channels for the given location. The device cannot transmit until it has checked that there are no incumbent devices on the transmission channel.
To broadcast a wireless signal in a white space, a user having a wireless device capable of wireless (e.g. radio) transmission in the white space needs to know which bands in the spectrum are occupied by or reserved for broadcasts by other devices to determine whether transmitting on a given band is permitted in the user's particular geographic location. For example, FIG. 2 shows a wireless device 201 connected to a central database 203 containing spectral allocation information. The database 203 provides the available channels in the spectrum for a given physical or geographical location. In order to legally transmit signals in the regulated spectrum in the given physical or geographical location, the wireless device 201 must be able to access and obtain spectral allocation information stored in the centralized database 203. However, the wireless device 201 must access the database 203 other than by the use of the regulated spectrum. Such a connection to the centralized database is typically made by wired or wireless Internet connections 202 and 204 (e.g., cellular, WiFi, WAN, satellite) or a direct connection 206 to the centralized database.
The requirement of having an Internet connection (e.g., 202) to connect to the centralized database places a number of burdens on users, including: being in a location which offers Internet access; purchasing an Internet connection; accessing the Internet; having a device which supports a wired or wireless Internet connection; etc. For example, a user must be in the range of a WiFi access point (AP) to connect to the AP, have the ability to authenticate with the AP (which usually involves a cost of some kind), and have a device which supports WiFi connectivity. Further, a user having an Internet connection such as a cellular network data connection is burdened with the cost and range of the cellular network. A direct connection to the centralized database (without accessing the Internet) may be possible in some cases, but is generally unlikely since direct connections to centralized databases are typically reserved for Internet service providers, distributors, large companies, etc. The cost of such a connection, if possible, may not be feasible for typical users transmitting with wireless devices.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.